Phytoosociology of floristic groups in subtropical seasonal forests in the south extreme of the Atlantic Forest Biome

This study aimed to differentiate the structure and flora of tree component groups of a stretch of forest at the southern end of the Atlantic Forest biome, Rio Grande do Sul. For sampling the tree layer (diameter at breast height ≥ 5.0 cm), 18 plots of 20 m × 10 m were systematically installed. Data were analyzed according to the structure and diversity of vegetation using the agglomerative hierarchical cluster analysis method with Ward linkage, and the quadratic Euclidean distance to measure dissimilarity. The formation of three groups of flora was evident. The species composition of each group belonged to different stages of natural succession. Group I had the highest species richness (42 species) and the highest species diversity (2.92 nats ind.-1). The species with the highest importance value index (IVI) were: in Group I, Actinostemon concolor (14.7%), Trichilia claussenii (VI = 9.8%), and Apuleia leiocarpa (8.9%); in Group II, Trichilia claussenii (21.2%), Sorocea bonplandii (18.1%), and Trichilia elegans (17.6%); and in Group III, Allophylus edulis (12.1%), Cupania vernalis (9.6%), and Trichilia claussenii (9.4%). The three groups showed a negative exponential diameter distribution, common in forests with auto-regeneration capacity